In conventional paging systems, each paging receiver is assigned a unique address. Whenever a paging message is transmitted, the system transmits the message in associate with the address of a particular paging receiver for which the message is intended. Each paging receiver in the system only accepts messages which include its address.
It is desirable that paging receivers provide very high reliability; however, environmental factors sometimes interfere with message reception and sometimes messages are lost. It has been suggested that it would be desireable if each message were numbered so that a user of a receiver could determine if a message had been missed. This is suggested in a report by the Post Office Code Standardization Advisory Group (POCSAG) entitled "Standard Message Formats for Digital Radio Paging", Autumn 1980. Message numbering was not made apart of the POCSAG standard which is discussed in the subject report. The group which prepared the report merely indicated that "message or segment numbering is recommended as a feature for paging system operators to offer as useful option". The authors indicated that numbers in "the cyclically rotating range 1-9 would be sufficient". There is no indication that the authors conceived a practical implementation for the suggested system.
Some prior art paging receivers which use the POCSAG protocol described in the above reference, do provide facilities for numbering messages. For example, U.S. Pat. Nos. 4,385,295, 4,412,217 and 4,803,487 provide systems which number messages. However, these receivers include memory mechanisms for storing messages and assigning each incoming message with a message number. The incoming message and the associated number are then stored in the receiver's memory. When the message is later retrieved for viewing, the message numbers also displayed, thereby aiding a pager user, or subscriber to the paging system, in keeping track of which messages have been reviewed.
U.S. Pat. No. 4,803,487 describes a different system which uses message numbering. In the systems shown in that reference, the display portion of the pager unit is separated from the receiver portion. The display portion is worn on the subscribers wrist, while the receiver portion is carried elsewhere on the subscribers person, apparently because the receiver is of two large a size to be comfortably worn on the receivers wrist. The receiver portion of this system includes message memory and includes a low powered transmitter for relaying the messages from the receiver portion to the display portion for display to the subscriber. The receiver assigns numbers as messages are received and provides the number information to the display along with the message.
The attachment of a number to a message at the receiver does nothing to alert the subscriber to the absence of a message if the message has not reached the subscriber. Nor does assigning a message number at the receiver provide any information which enables the receiver to determine if a message has been missed.
Unlike the prior art described above, in which the message numbers are assigned on receipt of the message, the transmitting system which is used with the present invention assigns the numbers to messages at origination, at the system's central clearing house facility. This message assignation system is described in co-pending Ser. No. 435,315, filed Nov. 13, 1989 to Gaskill et al.
The system described in the above-referenced, co-pending applications achieves a high degree of reliability by transmitting each message several times. In such a system, message numbering is used in a novel way to achieve synergistic results with the other parts of the system.